1. Field
The invention relates generally to injection devices, and specifically to injection devices having both a contact surface for attaching to a patient's skin and a cannula for piercing the patient's skin and introducing an injection fluid into the patient.
2. Description
As used throughout the specification, the term "injection" will encompass both relatively fast injection (bolus) and relatively slow introduction (occasionally called infusion or instillation) of a liquid into the body.
An injection device of the above kind is known in the art, for example from EP-A-272 530 which corresponds to U.S. Pat. No. 4,886,499, issued Dec. 11, 1989 to Cirelli, et al., the contents of which are herein incorporated by reference. Cirelli, et al. describes various embodiments of such an injection device which utilize various types of reservoirs and pumps. A common feature of all of Cirelli, et al.'s described embodiments is that the mechanical construction results in a device requiring a certain minimum overall height. A very small overall height is necessary for achieving acceptance by patients of devices worn on their bodies.
Another disadvantage of known injection devices in which the injection cannula is shot into the patient's skin is that the liquid connection between the cannula and the reservoir is prone to faults. These faults occur because of the relatively complicated construction needed to permit relative movement between the cannula and the reservoir. Such complicated construction also causes problems with regard to sterility and aseptic filling, especially with heat-sensitive preparations. Moreover, complicated connections of this type, in addition to being prone to breakdown, are so expensive as to make the devices unsuitable as throwaway articles.
Alternatively, if the reservoir and the cannula were to be fixedly connected, the entire reservoir would need to be accelerated for shooting the cannula into the skin, thus requiring far more driving power. Such a solution would therefore be uneconomic. Moreover, disposable or throwaway articles are preferable in many medical applications because it is often difficult to avoid premature discharge of injection solution or, conversely, suction of a small amount of blood, lymph, or the like.
Finally, known injection devices have no simple, reliable means for preventing damage to the cannula when the device is removed from the patient after the injection process.
A need exists for an injection device which does not have these disadvantages, and the subject invention addresses this need.